Phased-array antennas in conventional space-based radar systems that detect, identify and track targets near the Earth's surface are typically large monolithic antennas. These large arrays achieve high gains because if their large receiving aperture. Such phased-array antennas must use powerful transmitters and large, complex antennas to achieve a signal-to-noise ratio sufficient to perform moving target detection. Moreover, large supporting frames are required to hold large numbers of antenna array elements in a well-defined, fixed spatial orientation. The supporting frame adds to the mass and complexity of such systems.
The large number of antenna elements and the size of the supporting structure contribute significantly to the overall mass of space-based radar systems employing phased-array antennas. In addition, small deviations from the desired fixed array structure orientation cause significant loss in antenna gain, which greatly compromises system performance. As a result, space-based radar systems employing phased-array antennas are limited in flexibility, and difficult to deploy. In addition, phased-array antennas are expensive to manufacture, primarily because of the very large mass involved both in the antenna and its supporting structure.
Space-based array antennas are known. U.S. Pat. No. 4,843,397, for example, discloses a large distributed phased-array antenna for a space-based radar system. The antenna comprises a plurality of antenna array elements that are interconnected by a network of tensioning wires and pulling satellites to form a substantially planar, semi-rigid array. Each antenna array element is mounted on an individual elementary satellite that relays radar signals to a main satellite for processing and beam-forming.